1. Field of the Invention
This invention relates to a method for inhibiting the degradation of an acrylamide polymer and more particularly to a method of inhibiting the degradation of an aqueous solution of acrylamide polymer used in a petroleum recovery process.
2. Description of the Prior Art
Acrylamide polymers have found extensive use in many industrial fields as, for example, a sedimentation promotor, a soil conditioning agent, a paper-making chemical, an additive for electrolytic refining, an agent for reducing frictional resistance, a textile finishing agent, an oil-water separating agent, a chamical for oil recovery, and various caking agents, and new uses are developed every time there is a change or modification in the type or combination of the polymer.
The acrylamide polymers achieve the intended result in these many applications. However, because acrylamide polymers are generally more susceptible to degradation than other polymers, they frequently have not exhibited their inherent abilities to the fullest extent. For example, when an aqueous solution of an acrylamide polymer is allowed to stand at room temperature, in a relatively short period of time it often fails to retain the original viscosity. Particularly, this degradation tendency is accelerated at comparatively high temperatures, and in extreme cases, the polymer solution becomes useless for the intended application.
With this background, various investigations have been undertaken about degradation inhibitors for acrylamide polymers. For example, U.S. Pat. No. 3,337,356 and U.S. Pat. No. 3,493,539 teach that 2-(o-amido-phenyl)-2,1,3-benzotriazole or 2-(2-hydroxyphenyl)benzotriazole are effective as ultraviolet light absorbers.
When an aqueous solution of an acrylamide polymer is injected into the oil-bearing subterranean formation to recover oil, it is present in the oil-bearing subterranean formation (ranging from injection wells to production wells), which is generally at a temperature of about 40.degree. to about 120.degree. C., for long periods of several months to several tens of months. Accordingly, the oil recoverers demand quality assurance of the polymer during this period, and the suppliers of the acrylamide polymers are required to minimize the degradation of these polymers with time in the above temperature range. It is not until this problem is solved that the acrylamide polymers can be fully used to exhibit their inherent function.
The reduction of the quality of the acrylamide polymers under the oil recovering conditions is believed to be due to the disintegration or depolymerization of the polymers, but the mechanism has not yet been fully elucidated. It is generally thought to be based on a free radical reaction involving dissolved oxygen in water, etc. From this standpoint, U.S. Pat. No. 3,580,337 discloses the use of a water-soluble divalent metal salt such as sodium hydrosulfite as an oxygen scavenger in oil recovery, and U.S. Pat. No. 3,800,887 states that formaldehyde is effective as an oxygen scavenger.